Primer 52: The Program

Advanced Strategy for Muscle Growth and Fat Loss

Completely reshape your body with this sophisticated and straightforward diet and training plan.

Improving your body is full of catch-22 situations:

  • To build a lot of muscle you need to eat a lot, but that means you’ll likely gain some fat, too.
  • To lose a lot of fat you need a caloric deficit, which often negatively affects your training and can even lead to muscle and strength loss.
  • Training heavy will get you stronger and can make you more muscular, but it can drain you and abuse your joints and tendons.
  • You can build muscle by doing lighter work that’s easier on the nervous system and your joints, but you might lose strength in the process.

It’s also hard to mix and match the various ways you like to train, like sprinting, recreational sport, strength work, hypertrophy work, conditioning, etc. And it’s even harder trying to eat for the type of training you’re doing or have done.

All of the preceding is why Paul Carter and I developed a nutrition/training approach called “Primer 52.” It is in fact similar to The 5/2 Fat Loss Diet for Lifters devised by TC Luoma that uses two days of very aggressive caloric restriction and 5 days of maintenance or even surplus eating.

Primer 52, however, takes the idea further, focusing on fundamentals of advanced biochemistry and a specific combination of training and nutrition. The program is revolutionary in that it allows you do anything and everything you want to do as far as reshaping your body, either through increasing muscle, losing fat, or both. You literally eradicate all those catch-22s.

But before I lay out the specifics of Primer 52, I first need to list the three muscle growth factors (MGF) that are essential to muscle growth, along with explaining the value of caloric deficits and how we can easily manipulate mTOR and AMPK.

MGF 1 – You Don’t Need a Caloric Surplus to Build Muscle

Yes, you read that right. The “evidence-based” coaches will want to destroy me, but I have science to back me up when I say that you don’t need extra calories to build muscle. In fact, a caloric surplus isn’t even a main variable when it comes to building muscle. It’s only indirectly involved.

A couple of years ago, Dr. Stuart Phillips and a group of capable scientists from McMaster’s University recruited two groups of 20 men. Both groups were assigned a diet that gave them a 40% caloric deficit per day over 4 weeks. (All of their meals were given to them, so it was well controlled.)

One group had a daily protein intake of 1.2g/kg (0.54g per pound, so about 108 grams for a 200-pound man) and the second group received about twice as much protein, or 2.4g/kg (1.1g per pound, so about 220 grams for a 200-pound man).

All of the men lifted 4 days a week and did sprints 2 days a week. After 4 weeks, both groups lost a significant amount of fat (around 3.5kg or 7.7 pounds). The low protein group lost a small amount of muscle while the high protein group actually GAINED some muscle. (1)

Clearly, protein is the nutritional key necessary for muscle growth, and not a calorie surplus.

MGF 2 – You Need Sufficient Energy to Build Muscle

This factor may at first sound like it contradicts what I just wrote about not needing a caloric surplus to build muscle, but it doesn’t. Hear me out.

To build muscle you do need fuel. Constructing new muscle requires energy. You need 3 calories to synthesize 1g of protein, to be exact. There are 220g of protein in 1kg (2.2lbs) of muscle, so at the very least you’ll need 660 calories to synthesize enough protein to build a kilo of muscle.

But in reality it’s much higher than that because of the daily protein turnover (you break down and rebuild muscle tissue constantly). And the more you train, the higher that turnover is. While the exact number isn’t that important, it’s safe to say that you’ll need at least 1000 calories to fuel the process of building a kilo of muscle.

Again, this sounds like I’m saying you need a caloric surplus to build muscle, but you don’t. If you need more energy than you have consumed, you’ll simply dip into your reserves (stored body fat or glycogen). It’s the same thing with building muscle. If you need energy to fuel the process but you’re in a deficit, you’ll use stored energy to get the job done.

This is also why the leaner you are, the harder it is to build muscle while being in a deficit. Fatter individuals have a lot more reserves and there’s no threat to your survival if you use that stored energy to fuel muscle growth.

MGF 3 – You Need To Actually Stimulate Protein Synthesis

It’s not enough to have sufficient protein available to build muscle and the energy to fuel the process. If you don’t trigger an increase in muscle protein synthesis, you won’t build muscle.

And this is where the caloric surplus plays a role, albeit indirectly, by increasing both insulin (which happens if you eat more carbs and proteins) and IGF-1 (the liver needs insulin and growth hormone to release IGF-1). Raising insulin is important because it both decreases muscle protein breakdown and stimulates protein synthesis by increasing mTOR.

Note that resistance training itself raises mTOR and it can also increase local IGF-1 if the muscle fatigue/lactate release is high enough, which is why frequency of training can be important when trying to build muscle.

If you can release IGF-1 and increase mTOR at the right times, and you have sufficient protein available, you can build muscle even if you aren’t in a surplus. Primer 52 uses mTOR maximization days to trigger growth, along with days where it’s kept low on purpose to favor health, fat loss, and anti-aging effects.

The Role of Caloric Deficits in Losing Fat

Christian Thibaudeau bench

One thing that’s 100% correct about losing fat: you do need to be in a state of caloric deficit. It’s not the only thing that matters, but if you’re not in a deficit the other things won’t matter.

Yes, insulin sensitivity plays a role. The more sensitive you are to the hormone, the less likely you are to decrease stored energy (fat) in the hours after a meal.

To lose a pound of fat you likely need to be in a deficit of close to 7000 calories. (2)

The typical way of doing things is to create a small/moderate daily deficit – maybe a 500-750 calorie deficit per day – for 7 days.

However, if you create the same total deficit over fewer days, two days for example, the fat loss will be the same. In fact, in the long run this method might result in even greater fat loss because there’s less chance of a reduction in the body-weight regulating hormone leptin because you’re not constantly in a deficit.

That’s what Primer 52 does: Create a large caloric deficit 2 days a week, along with 2 days where you eat a surplus; two days where you eat maintenance calories or at a slight deficit (depending on your goal); and one day of moderate/small deficit. The training is accordingly planned to fit the way you’re eating on that day.

But it’s actually a lot more elegant than simply waving the caloric-intake wand. We actually manipulate two of the body’s key enzymes.


Both mTOR and AMPK are enzymes that play key physiological roles. They’re normally seen as being antagonists (opposed to each other) as AMPK can inhibit the action of mTOR.

While mTOR is normally seen as a positive enzyme when it comes to building muscle, it’s not all happiness and blue skies. Speeding up cellular growth is great for muscle mass, but excessive mTOR activity can also have negative drawbacks like speeding up the growth of cancerous cells and premature aging.

AMPK, on the other hand, increases glucose and fatty acid uptake and oxidation when energy intake is deficient (so it can help you lose fat). It decreases the creation of new fat cells (adipocyte lipogenesis) and increases fat breakdown.

But even more interesting is that a lot of recent research has established a strong connection between AMPK and aging. When we get older we become less responsive to AMPK, which leads to: 1) less orderly cell recycling (autophagy), 2) increased oxidative stress, 3) increased low-grade systemic inflammation, 4) increased fat storage, 5) high blood sugar, and 6) greater incidence of metabolic syndrome. (3)

As such, we have to carefully manipulate the two enzymes. As far as mTOR, we favor its expression when:

  • Caloric intake is higher (surplus)
  • Carbs/insulin are higher
  • Protein/amino acids, especially leucine, valine, isoleucine and glycine, are high
  • We do resistance training

Conversely, we favor AMPK expression when the conditions that favor mTOR expression are more or less reversed:

  • Caloric intake is lower (deficit)
  • Energy output is higher
  • Carbs/insulin are kept low
  • Amino acids are kept low
  • You do cardio work

This is simplistic but it’s precise enough for our purposes here. So how do you reconcile building muscle (favoring the mTOR system) and extending lifespan and health (which favors the AMPK system)? That is where the Primer 52 system comes in.

Primer 52 Overview

Christian Thibaudeau bar

Primer 52 involves 3 (or 4) different types of days, each employing a different strategy to take advantage of the enzyme systems. The type of training you select is up to you, as are the food choices, but here are some recommendations:

1. AMPK/Fasting Days

Here the goal is to get the greatest AMPK activity possible. This will help slow down aging, increase fat oxidation, reduce systemic inflammation, and maintain insulin sensitivity.


It’s pretty simple. You fast for at least 24-hours on these days.

For example, you’d stop eating the previous day at 6 PM and have only a small protein/fat meal at 8 PM on the fasting day itself. Paul Carter prefers a 24-hour fast, while I go whole hog and continue the fast until the next morning (that equates to about 34-36 hours of fasting).

Refrain from any liquids containing calories (black coffee is fine). Also, don’t take any protein/amino acid supplements. You can fast until the next morning or have a small protein/fat meal at 8-9 PM (something like 4-6 oz. of beef and some green veggies).


No lifting on that day.

It makes no sense to train if you don’t have amino acids available to repair the damage. You can, however, do cardio, HIIT, sprints, walking, yoga, mobility work, etc. Any low intensity activity is fine.

2. Hypertrophy/mTOR Days

Here the goal is maximum hypertrophy and protein synthesis via a large increase in mTOR activation, especially around workouts.


This is a caloric surplus day with high carbs and high protein (low fat).

You should ingest roughly a 15-20% caloric surplus (a good starting point is 18-19 calories per pound of body weight) with 1.25 – 1.5g of protein per pound and 80% of your non-protein calories coming from carbs and 20% from fats.

I recommend allocating 50% of your daily carbs around the workouts (pre-, intra-, and post-); 25% in the evening; and the rest spread across the other 2-3 meals.


This is a typical bodybuilding day.

Your reps per set should fall between 8 and 15, 6 to 8 exercises (not per muscle, but for the whole workout) for 3-5 sets each. You can use typical hypertrophy methods like supersets, drop sets, mechanical drop sets, rest/pause, myo reps, etc.

3. Strength Days

This is when we focus on neurological training, i.e. heavier work. We don’t need to activate as much mTOR here as we do for the hypertrophy days.


Eat anywhere between a small deficit to a small surplus depending on your main goal.

A good starting point is 15-16 calories per pound of body weight with 1–1.25g of protein per pound, and 80% of your non-protein calories coming from fats and 20% from carbs. The carbs should be consumed during the peri-workout period.


Think powerlifting, maybe a 5/3/1 or a conjugate/Westside max-effort day set up.

The key is fewer exercises (3-5), big compound movements, heavier loads (sets of 1-6 reps), and longer rest intervals.

You can use supramaximal methods like heavy partials or isometrics. You can also use heavy loaded carries (farmers walk, Zercher carries, Prowler pushing).

4. “Adaptable” Days

This isn’t really a fourth type of day but more like a day where you can do the type of work/nutrition you want, based on your goal:

  • If your main goal is fat loss, go low carb, high protein, moderate fat, and do a sprint session.
  • If your main goal is muscle growth, do a third mTOR day with hypertrophy work for your weaker body part(s).
  • If your main goal is strength, do a third strength day with low carbs/moderate fats/high protein intake.
  • If your main goal is longevity/health, do an energy system work combo (sprints, strongman, cardio, HIIT, etc.) on a caloric deficit with low carbs and moderate-low protein.

As far as calories, a good starting point is 12-14 calories per pound of body weight with a 0.85-1.0 g of protein per pound, and 80% of your non-protein calories coming from fats and 20% from carbs. (The carbs should be consumed during the peri-workout period.) You can adjust the calorie intake up or down depending again on your goals.

But if you choose to use this “adaptable” day as a third hypertrophy day, the nutrition would be the same as described for the other hypertrophy workouts.

Note: You don’t have to treat this day as either another strength day or a hypertrophy day. Alternately, you could go with what I call “athletic” training, i.e., do things like sprints, jumps, throws, Olympic lifts, etc.

Primer 52 Weekly Set Up


The days are set up so that each day primes the body for the next day. For example, the fasting day increases the anabolic response to the high protein/high carbs you’ll employ the next day. The high carbs load you up and make you stronger on the strength days. The low carb/high fat days make the fasting days more effective at AMPK activation.

Here’s what a typical week looks like:

  • Sunday: Fasting/Cardio (AMPK activation day)
  • Monday: Upper-body hypertrophy/high carbs/high protein/low fat (mTOR activation day)
  • Tuesday: Lower-body strength/low carbs/high protein/moderate fat
  • Wednesday: Fasting/Cardio (AMPK activation day)
  • Thursday: Lower-body hypertrophy/high carbs/high protein/low fat (mTOR activation day)
  • Friday: Upper-body strength/low carbs/high protein/moderate fat
  • Saturday: Sprints or strongman/low carbs/moderate protein/moderate fat (Adaptable day)

Note: You can fast on different days (e.g. Tuesday/Saturday), but you would always position the hypertrophy/mTOR days on the subsequent days.

What Primer 52 Will Do for You

Primer 52 is the simplest way to build muscle and lose fat at the same time while improving several health markers. I also find it to be a very forgiving of the occasional cheat day (hopefully occurring only on your hypertrophy days).

Once you get in the groove of things, you’ll find that it’s the simplest and easiest way to get everything you want, physique-wise.

Metabolic Drive Metabolism Boosting / Award-Winning Protein




  1. Longland TM et al. Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss: a randomized trial. Am J Clin Nutr. 2016 Mar;103(3):738-46. PubMed.
  2. Hall KD et al. Energy balance and its components: implications for body weight regulation. Am J Clin Nutr. 2012 Apr;95(4):989-94. PubMed.
  3. Salminen A et al. AMP-activated protein kinase (AMPK) controls the aging process via an integrated signaling network. Ageing Res Rev. 2012 Apr;11(2):230-41. PubMed.

What are your thoughts on doing a MAG-10 fast on one of the fasting/ampk days? I was thinking Wednesday MAG-10 Fast, Hypertrophy Thursday.